It’s been a policy of Find-A-Grave for a long time to only allow HTML links to other Find-A-Grave memorials with links to other websites were not allowed. However, some ignored the rule and used HTML to other sites. As of sometime in July 2018, they shut down most of those HTML links and will remove any that were missed as they become aware of them. Note: you can still use HTML to link to other Find-A-Grave memorials.
From the FAQs:
Genealogical information about the subject can be included in the biography.
The biography is to be about the memorialized person with preference to an original biography. If a cause of death is included, it is to be short and to the point, and as shown on the death certificate. The bio must not look like a case file. Graphic bios are not acceptable.
Links to other websites or email addresses are not allowed within any memorial.
These standards will be added to and updated from time to time. Find A Grave reserves the right to edit any biography submitted to the site to conform to these and any future posted standards.
The issue was raised in the Find-A-Grave forums: https://www.findagraveforums.com/topic/15233-html-links-are-gone/ (you need to be a member of the Forums and logged in to access this link – it includes a link to a memorial where the HTML code has been removed).
In looking at the Wayback Machine, it appears the change occurred after July 30, 2008 (as that archived page doesn’t mention it) and before September 1, 2008 (which specifically mentions not including website addresses from obituaries): https://web.archive.org/web/20080901083436/http://www.findagrave.com:80/cgi-bin/fg.cgi?page=listFaqs
Can I add an obituary to my interment listing?
In general, obituaries in newspapers are placed by the family and can be placed as part of the biography on Find A Grave as long as it lists the newspaper and date the obit was printed. Those for “famous” individuals are usually written by newspaper staff and can not be posted to Find A Grave.
Please do not include website addresses that may be listed in the obituary as they usually expire within a year after the obituary is printed.
While it specifically mentions website addresses in the obituary, it would later be clarified to include any website in the Bio field or in the Flowers/Token section. Many obituaries were added verbatim from newspaper or funeral websites that often included links to the funeral home. I always removed those links when I added obits submitted by other contributors or when I rewrote the obituary in my own words to avoid copyright issues if I was adding it from an obituary I had found.
No doubt some will try and figure out how to get around the link issue, but in my opinion, it’s best to give people sources where they can find more information. For example, mentioning in the Bio that Wikipedia has more about the individual is a good way to have people who are interested in more information check Wikipedia. It appears they haven’t removed the URL from the above memorial, but only the HTML that allowed one to click on it. You could copy/paste the URL into a browser and it should work fine.